An FA (Factory Automation) technology in which a control device such as a PLC (Programmable Logic Controller) is used becomes widespread in various production sites. For example, as disclosed in Unexamined Japanese Patent Publication No. 2010-170536, the control device repeatedly performs a series of pieces of processing such as input and output refresh processing, common processing, user program execution processing, and peripheral service processing.
The control device is being made intelligent with recent progress of Information and Communication Technology (ICT). Along with the intelligent control device, the control device performs more pieces of processing (a task or a process). Because of a limited resource of the control device that performs the pieces of processing, it is necessary to efficiently use the resource.
Unexamined Japanese Patent Publication No. 2010-170536 pays attention to equalization of an execution interval of the sequential input and output refresh processing irrespective of factors such as a variation in execution time necessary for a user program, but does not consider the above problem.